Introduction to Polar Cap Patchesby Jøran Moen

Chapter 4 from the compendium is essential to understand production, loss, and transport of ionospheric plasma!!

Clouds of high electron density form near the cusp inflow region on the dayside. They form and enter the polar cap in association with magnetopause reconnection

Solar EUV ionization is the main production mechanism for high density electron patches (clouds). When they enter the polar cap they stay in sharp contrast low-density plasma there

The patches are frozen into the plasma motion (ExB-drift), and convect with the polar cap twin cell flow from day to night.

The patches can be observed by radar and by ground based optics. Recombination of O+ gives rise to 630.0 and 557.7 nm emissions.

The only way for these patches to exit the polar cap is due to tail reconnection; then they can cross the OCB.

OUTLINE: • Neutralization of

electron patches and airglow

• 630 nm airglow observations in the 18-06 MLT sector

• Combined all-sky and SuperDARN convection maps

Neutralization of O+ and airglow• Key processes:

hOO

OOeO

OOOO

ONONOk

k

*

*2

22

2

2

1

• In the F-region: One

Neglecting production and transport in the continuity equation we have:

lt

O

i.e. O+ or the electron density is controlled by the loss term l

airglow

2

4.030017

2

2

300

20

1

2221

0

2221

329.0

100.2

100.8

0

ETT

k

k

OkNk

where

enn

e

dt

OkNkt

neff

T

T

tee

t

O

eff

eff

OO

O

O

O

Decay of electron density/O+

Core instrumentation for UiO patch studies:

ARR

LYRNYA

Polar cap patches:• Major source:

Solar EUV ionized plasma

• Patch definition by density: Ne = 2 x Neo

• By airglow intensity: Recombination of O+

50R above 630nm background

• Horisontal scale 100-1000 km

• Altitude of Airglow emissions:~300 km

TEC image demonstrating transport of EUV ionized plasma that extends into the polar cap (Foster et al., 2005)

The only way to exit patches from the polar the polar cap is by tail reconnection

06

12 MLT

24

18

MSP

70

80

Svalbard – is an ideal platform for studying airglow patches at night

High-density patches formed in the Canadian/ American cusp sector drift at us at night

06

12 MLT

24

18

MSP

70

80

Occurence rate of polar cap patches

Eight winters (1997-2005) of MSP data from Ny-Ålesund have been analyzed

43 nights, 333 events

About 60% of the patches exit the polar cap from 22-01 MLT, but patches was observed in the entire MLT range from 18:00-05:00.

06

12 MLT

24

18

MSP

70

80

Moen et al., GRL2008

A new tool for studying tail-reconnection dynamics

NOTE:• Patches exit the polar cap in the entire MLT range of

tail reconnection (18-05 MLT)• All-sky and radar tracking of patches provides a new

tool to study tail reconnection dynamics. I.e. to observe how thet cross the OCB – the poleward border of the night-time auroral oval.

• As high density plasma clouds tend to be turbulent, they are an important space weather phenomenon for communication and navigation systems. See next slide.

• With the ICI-series of sounding rockets, UiO specializes on in-situ measurements of polar cap patches. ICI-3 will be launched from Svalbard winter 2011, and ICI-4 is planned to fly over Svalbard near solar maximum in 2014.

QuickTime™ and aYUV420 codec decompressor

are needed to see this picture.

Of relevance to satellite navigation

• Turbulence and irregularities in the ionosphere give rise to scintillations in the satellite to ground signal

• The Total Electron Content (TEC) along the path of a GPS signal can introduce a positioning error ( up to 100 m)

• More severe in the arctic regions• The effects on GPS can be one of the most

important space weather phenomena for Norway as the Barents sea opens for offshore activities and the East-West passage is likely to open due to sea ice meltdown

Universitetet i Uppsala i 1983

ICI-2&3

Investigation of Cusp Irregularities